Reconstruction of paleohydrogeological conditions in the late Holocene based on the study of calcareous tufa in the spring mire of the Wolborka River drainage basin (central Poland)

The article presents the results of research on spring mire cupolas of the Wolbórka River, a left tributary of the Pilica River. The sedimentary sequence overlies fluvial sands and includes three series of calcareous tufa separated by peat layers. 14C dating indicates that the sedimentation in the spring mire area began in the late Atlantic (AT) and ended at the end of the Subboreal period (SB2). Analysis of lithological features of the sediments has allowed the reconstruction of environmental conditions and their impact on the functioning of the groundwater outflow zone in the late Holocene. The mutual relationship between the peat layers and successive series of calcareous tufa records the changes in humidity conditions resulting from periodic changes in climatic conditions. The sediments of the spring mire cupolas, which are composed mostly of calcite, also contain gypsum and pyrite. The ratio of gypsum to pyrite has proven to be a useful tool for reconstructing humidity condictions. It has become the basis for demonstrating that calcareous tufas are sediments of dry periods, and the deposition of cupola sediments depended on the hydrodynamic regime and flow rate of the springs. The main factor contributing to the deposition of calcite was the equilibration of the groundwater solution with the partial pressure of carbon dioxide in the atmosphere, at low flow dynamics.